This invention relates to dry, powder electrophotographic toners suitable for multicolor and single color or black imaging.
Toners suitable for multicolor imaging avoid employing dark ingredients, as dark masks the intended color. Silicon carbide is dark and cannot be used, even in the small amounts it is typically used, as ingredient on the surface of toner particle (often termed an extra particulate additive or EPA).
The function of the silicon carbide in prior toners was as an abrasive to scrub the contact surface of the doctor blade. Instead of silicon carbide, this invention employs a material believed entirely novel as an EPA. The material is rutile acicular titanium oxide with aluminum oxide surface treatment.
The embodiment described in detail in this application is operative at relatively low fusing temperatures so as to facilitate multicolor imaging on transparencies. Consistent with such low temperatures, the wax component of the toner, which is for release of toner from the fuser, can be of relatively low molecular weight (500 Mn in the embodiment). Additionally, this embodiment contains two amorphous silica particles in the bulk. The first particle, having a BET specific surface area of about 3xc2x115 m2/gm, is rendered hydrophobic. The second particle, having a BET specific surface area of about 380 m2/gm is not surface treated. The incorporation of these particles in the bulk of the toner allows the toner to survive temperature and humidity extremes during storage and shipping without caking or blocking and the associated print quality flaws. This is desirable as toners, especially low melt toners, must be robust to shipping and storage conditions in order to be attractive to a world-wide market.
The embodiment of this application can employ a mixture of charge control agents, specifically an organoboron complex negative charge control agent and a quaternary ammonium salt of an aluminosilicate negative charge control agent; the combination providing consistent flow of the toner having branched polyester resin as the binder. This consistency of toner flow is both throughout the life of the toner and with toners of different colors, independent of printing environment (temperature and humidity). This provides multilayer uniformity for color applications in which toners having subtractive colors are layered over each other.
In a generally conventional, dry, particulate electrostatic toner having polyester resin as a binder, pigment as a colorant, charge control ingredients, wax as a release agent, and extra particulate additives (EPAs) to improve flow and to scrub contacting elements such as the doctor blade: 1) one EPA is hydrophilic rutile acicular titanium oxide with aluminum oxide surface treatment; 2) two silicas are blended within the bulk of the toner one of low surface area and one of high surface area; and 3) the charge control element is a blend of an organoboron complex negative charge control agent and a quaternary ammonium salt of an aluminosilicate compound.
The acicular titanium oxide provides a new advantage of more reliable toner flow (eliminates toner xe2x80x9cstarvingxe2x80x9d), and this advantage, as well as the scrubbing function, is similarly realized using the acicular titanium oxide with a black toner having carbon black or magnetite or both as the pigment. Similarly, similar functioning for the acicular titanium oxide has been found with toners which contain neither the foregoing dual silicas nor the foregoing charge control agents.
Similarly, the inclusion of dual, blended-in silicas is believed to be a function of the silica size and surface treatment and therefore to be applicable to a wide range of toners.
Finally the blend of charge control agents is believed to exhibit synergistic interaction with a polyester binder not dependent on the other elements to provide consistent toner flow. Such efficacy has been demonstrated with the weight ratio of the organoboron complex to the aluminosilicate being from 2 to 1 to 1 to 2.